The first automatic transmissions was developed in 1904 by the Sturtevant brothers of Boston, Massachusetts.  It had two forward speeds, selected by flyweights driven by the engine.  At higher engine speeds, high gear was engaged.  As engine RPM decreased, the gearbox would shift back to low.  Unfortunately, owing to the abruptness of the gear change, the transmission would often fail without warning.

In 1908 with the introduction of the Ford Model T, a simple, two speed plus reverse planetary transmission, manually controlled by the driver using pedals was used.  The pedals actuated the transmission’s friction elements (bands and clutches) to select the desired gear.

In 1934, both REO and General Motors developed semi-automatic transmissions that were less difficult to operate than a full manual unit.  However, they continued to use a clutch to engage the engine with the transmission.  The General Motors unit was notable in that it employed a power-shifting planetary gearbox that was hydraulically controlled and was sensitive to road speed, anticipating future fully automatics.  Parallel to the development of automatically shifting gearbox by REO and GM was Chrysler’s work on adapting the fluid coupling to automotive use.  Invented early in the 20th century, the fluid coupling was the answer to the question of how to avoid stalling the engine when the vehicle was stopped with the transmission in gear.  Chrysler itself never used the fluid coupling with any of its later automatic transmissions, but did use it in conjunction with a hybrid manual transmission called “Fluid Drive” and the similar “Hy-Drive” which used a torque converter.

These developments in automatic gearbox and fluid coupling technology eventually culminated in the introduction in 1939 of the General Motors Hydra-Matic, the world’s first mass-produced fully automatic transmission.  Available as an option on 1940 Oldsmobiles, the Hydra-Matic combined a fluid coupling with three hydraulically controlled planetary gear sets to produce four forward speeds plus reverse.  The transmission was sensitive to engine throttle position and road speed, producing fully automatic up- and down-shifting that varied according to operating conditions.  The Hydra-Matic was subsequently adopted by Cadillac and Pontiac, and was sold to various other automakers, including Bentley, Hudson, Kaiser, Nash, and Rolls-Royce.

From 1950 to 1954, Lincoln cars were also available with the Hydra-Matic.  Mercedes-Benz subsequently devised a four-speed fluid coupling transmission that was similar in principle to the Hydra-Matic, but of a different design.  In 1956, GM introduced the “Jetaway” Hydra-Matic, which was different in design than the older model.  Addressing the issue of shift quality, which was an ongoing problem with the original Hydra-Matic, the new transmission utilized two fluid couplings, the primary one that linked the transmission to the engine, and a secondary one that replaced the clutch assembly that controlled the forward gearset in the original.  The result was much smoother shifting, especially from first to second gear, but with a loss in efficiency and an increase in complexity.  Another innovation for this new style Hydra-Matic was the appearance of a Park position on the selector.  The original Hydra-Matic, which continued in production until the mid-1960s, still used the Reverse position for parking pawl engagement.

The first torque converter automatic, Buick’s Dynaflow, was introduced for the 1948 model year.  It was followed by Packard’s Ultramatic in mid-1949 and Chevrolet’s Powerglide for the 1950 model year.  Each of these transmissions had only two forward speeds, relying on the converter for additional torque multiplication.

In the early 1950s, BorgWarner developed a series of three-speed torque converter automatics for American Motors, Ford Motor Company, Studebaker, and several other manufacturers in the US and other countries.  Chrysler was late in developing its own true automatic, introducing the two-speed torque converter PowerFlite in 1953, and the three-speed TorqueFlite in 1956.  The latter was the first to utilize the Simpson compound planetary gear set.  General Motors produced multiple-turbine torque converters from 1954 to 1961.  These included the Twin-Turbine Dynaflow and the triple-turbine Turboglide transmissions.  The shifting took place in the torque converter, rather than through pressure valves and changes in planetary gear connections.  Each turbine was connected to the drive shaft through a different gear train.  These phased from one ratio to another according to demand, rather than shifting. The Turboglide actually had two speed ratios in reverse, with one of the turbines rotating backwards.  By the late 1960s, most of the fluid-coupling four-speed and two-speed transmissions had disappeared in favor of three-speed units with torque converters.

By the early 1980s, these were being supplemented and eventually replaced by overdrive-equipped transmissions providing four or more forward speeds.  Many transmissions also adopted the lock-up torque converter (a mechanical clutch locking the torque converter pump and turbine together to eliminate slip at cruising speed) to improve fuel economy.

 Sidebar: Studebaker’s first Automatic transmission called “Automatic Drive” was a Studebaker designed and Borg Warner (Detroit Gear) built three speed automatic released the second half of the 1950 model year.